共查询到20条相似文献,搜索用时 15 毫秒
1.
The reserve ovary model is a key hypothesis proposed to explain why plants produce surplus flowers and posits that plants may utilize surplus flowers
to compensate for losses from floral herbivory. We tested this hypothesis in the prairie plant Eryngium yuccifolium and its floral herbivore Coleotechnites eryngiella. At five Illinois tallgrass prairie sites, we collected central, primary lateral, and secondary lateral inflorescences from
E. yuccifolium to determine whether damage by the larvae of C. eryngiella to the flowers in earlier developing inflorescences would be compensated for in later developing inflorescences. Coleotechnites eryngiella does extensive damage to the central and primary inflorescences and little damage to the secondary inflorescences. Later
maturing inflorescences did not compensate for early damage by increasing seed production in later inflorescences. The secondary
inflorescences of E. yuccifolium may only compensate for catastrophic damage done to the central and primary inflorescences early on in development, serve
as additional advertisements for pollinators, act as pollen donors, or allow the plant to take advantage of “ecological windows”
of high pollinator and low herbivore abundance. Our findings were spatially and temporally consistent and did not support
the predictions of the reserve ovary model in the E. yuccifolium–C. eryngiella system suggesting that in this system, alternate, proximate, and ultimate causes need to be explored for the production of
surplus flowers. 相似文献
2.
We examined the effects of leaf herbivory by the dorcas gazelle, Gazella dorcas, on the compensatory growth of the geophyte Pancratium sickenbergeri (Amaryllidaceae) in the Negev desert, Israel. In three populations exposed to different levels of herbivory, we removed different
amounts of photosynthetic leaf area from plants in five clipping treatments: 0, 25, 50%-dispersed over all leaves, 50%-entire
area of half the leaves, 100%. The population with the lowest level of herbivory showed the lowest relative regrowth rate
after clipping. In the population with a constantly high level of herbivory, plants in intermediate-clipping treatments overcompensated
in leaf area after clipping. For all the populations, clipped plants produce more new leaves than unclipped plants. In the
population with the highest level of herbivory, clipping treatments did not have a significant effect on the number of fruits
per plant. In addition, we did not find a trade-off between investments in growth and reproduction in this population. Our
results indicated that, in the desert lily, herbivores may select for plant mechanisms that compensate after damage as a tolerant
strategy to maintain fitness. 相似文献
3.
On northeastern Pacific coasts, Ulvaria obscura is a dominant component of subtidal “green tide” blooms, which can be harmful to marine communities, fisheries, and aquaculture facilities. U. obscura is avoided by herbivores relative to many other locally common macrophytes, which may contribute to its ability to form persistent blooms. We used a bioassay-guided fractionation method to experimentally determine the cause of reduced feeding on Ulvaria by echinoderms, molluscs, and arthropods. Our results indicated that dopamine, which constituted an average of 4.4% of the alga’s dry mass, was responsible for decreased feeding by sea urchins (Strongylocentrotus droebachiensis). Subsequent experiments demonstrated that dopamine also reduced the feeding rates of snails (Littorina sitkana) and isopods (Idotea wosnesenskii). Dopamine is a catecholamine that is a common neurotransmitter in animals. The catecholamines dopamine, epinephrine (adrenaline), and norepinephrine also occur in at least 44 families of higher plants. The functions of catecholamines in plants are less well known than in animals but are likely to be diverse and include both physiological and ecological roles. Our results are the first experimental demonstration of a plant or algal catecholamine functioning as a feeding deterrent. This novel use of dopamine by Ulvaria may contribute to the formation and persistence of harmful Ulvaria blooms in northeastern Pacific coastal waters. 相似文献
4.
Plant–herbivore interactions have strong ecological and evolutionary consequences, but have been traditionally overlooked
in marine higher plants. Despite recent advances in seagrass ecology that highlight the importance of herbivory, the mechanisms
that regulate the feeding behaviour of seagrass consumers remain largely unknown. Herbivores have been shown to reduce the
sexual reproductive success of seagrasses through direct consumption of inflorescences and seeds, but we know little about
intraspecific variation in susceptibility to grazing of different seagrass tissues. We contrasted the relative palatability
of reproductive and vegetative tissues of the temperate seagrass Posidonia oceanica in the field, and we assessed the feeding preferences among these tissues of the main consumers of the plant, the fish Sarpa salpa and the urchin Paracentrotus lividus. Moreover, we identified the plant traits that explained the observed feeding behaviour. We provide strong evidence for herbivore
selectivity among seagrass tissues. In the field, 70–90% of inflorescences were damaged by herbivores compared to 3–60% of
leaves of similar age. In feeding assays, the urchin P. lividus showed over a twofold preference for reproductive tissue at various stages of development. By contrast, we detected no feeding
activity on either leaves or inflorescences from the fish S. salpa, which is known to migrate to deeper waters soon after flowering starts and during the period of fruit maturation. Despite
being the preferred food of urchins, inflorescences were chemically defended, had higher levels of phenolics and lower nutrient
and calorific content than leaves. We experimentally demonstrated that leaf structural defences are the primary factor in
determining urchin feeding preferences. Removal of plant structure results in a drastic shift in urchin selectivity towards
the most nutritious and less chemically defended leaf tissue, indicating that multiple mechanisms of defence to herbivory
may coexist in seagrasses. 相似文献
5.
Trophic cascades may purportedly be more common in aquatic than terrestrial food webs, but herbivory on freshwater vascular
plants has historically been considered low. Water lilies are an exception, suffering severe grazing damage by leaf beetles.
To test whether a central prediction of cascade models—that predator effects propagate downwards to plants—operates in a macrophyte-based
food web, we experimentally manipulated predation pressure on a key herbivore of water lilies in the littoral zone of a lake
in Michigan, USA. Field experiments comprised combinations of caging treatments to alter the number of predators (larvae of
the ladybird beetle Coleomegilla maculata) that hunt the grazers of the macrophytes (larvae of the leaf beetles Galerucella nymphaeae) on the leaves of the water lily Nuphar advena. Predatory larvae of the ladybird beetles significantly reduced grazing damage to water-lily leaves by 35–43%. The predators
reduced plant damage chiefly via density-mediated effects, when lower densities of grazers translated to significant declines
in plant damage. Plant damage caused by the surviving herbivores was less than predicted from individual grazing rates under
predator-free conditions. This suggests that trait-mediated effects may possibly also operate in this cascade. The observed
strong effect of predators on a non-adjacent trophic level concurs with an essential component of the trophic cascade model,
and the cascade occurred at the ecotone between aquatic and terrestrial habitats: Nuphar is an aquatic macrophyte with emergent and floating leaves, whereas both beetle species are semi-terrestrial and use the
dry, emergent and floating leaves of the water lily as habitat. Also, the cascade is underpinned by freshwater macrophytes—a
group for which trophic processes have often been underappreciated in the past. 相似文献
6.
Tree species can affect the soil they are growing on and this might influence their fitness. The New Zealand gymnosperm tree
species kauri (Agathis australis (D. Don) Lindl.) which grows in mixed angiosperm–gymnosperm forests has a substantial effect upon the soil. We studied the
hypotheses that: (1) low soil moisture availability below mature kauri trees hampers growth of kauri seedlings and angiosperm
seedlings, (2) low nutrient availability below kauri trees hampers only angiosperm seedlings, and (3) angiosperm seedlings
are hampered more than kauri seedlings by the conditions below kauri trees. We tested these hypotheses by planting seedlings
of kauri and mapau (Myrsine australis (A. Rich) Allan) under kauri trees and applying the following treatments: removal of herbs, removal of litter, removal of
nutrient limitation, and elimination of root competition of mature kauri trees. The results indicate that low soil moisture
availability, or the combination of low soil moisture availability and low nutrient fertility, hampers the growth of kauri
as well as mapau seedlings below kauri trees. The mapau seedlings are hampered relatively more than the kauri seedlings which
might result in an increased relative fitness of the latter. 相似文献
7.
8.
Rien Aerts 《Polar Biology》2009,32(2):207-214
Global warming will lead to increased nitrogen supply in tundra ecosystems. How increased N supply affected leaf production,
leaf turnover and dead leaf N input into the soil of Empetrum nigrum and Andromeda polifolia (evergreens), Eriophorum vaginatum (graminoid) and Betula nana (deciduous) in a sub-arctic tundra in northern Sweden between 2003 and 2007 was experimentally investigated. There was considerable
interspecific variation in the response of leaf production to N addition, varying from negative, no response to a positive
response. Nitrogen addition effects on leaf turnover also showed considerable variation among species, varying from no effect
to increased leaf turnover (up to 27% in Eriophorum). Nitrogen addition resulted in a four to fivefold increase in N content in the dead leaves of both evergreens and a 65%
increase in Eriophorum. Surprisingly, there was no increase in Betula. The response of dead leaf P contents to N addition was rather species specific. There was no response in Empetrum, whereas there were significant increases in Andromeda (+214%) and Eriophorum (+32%), and a decrease of 47% in Betula. As an overall result of the changes in leaf production, leaf turnover and dead leaf N and P contents, nitrogen addition
increased in all species except Betula the amount of N and, for Andromeda and Eriophorum the amount of P transferred to the soil due to leaf litter inputs. However, the way in which this was achieved differed substantially
among species due to interspecific differences in the response of the component processes (leaf production, leaf turnover,
dead leaf nutrient content). 相似文献
9.
Darcy-Hall TL 《Oecologia》2006,148(4):660-671
The relative effects of nutrients and herbivores on primary producers are rarely compared across ecosystems that vary in potential primary productivity. Furthermore, proposed mechanisms to explain such patterns remain understudied. Here, I examine the strength of nutrient and grazer (herbivore) limitation (i.e., the extent to which producers’ growth is limited by insufficient nutrient supply or herbivory) of benthic algae across 13 southwest Michigan lakes that vary widely in productivity (i.e., resource supply). I compare the observed patterns of algal limitation and species composition to those predicted by two simple models: one that includes multiple species and species’ traits (the food-web model) and one that includes no variation in species or traits (the food-chain model). Species in the food-web model are assumed to display a tradeoff between resource competitive ability and resistance to herbivory (the “keystone predator” tradeoff). Among these lakes, benthic algal nutrient limitation was positive
and declined significantly along a lake N:P gradient. In contrast, grazer limitation was negative
and was not significantly related to any of the measured lake productivity variables. Negative grazer limitation indicated that the removal of grazers caused unexpected declines in algal biomass, which were potentially due to indirect, positive effects (e.g., nutrient recycling) of grazers. Nutrient limitation was significantly stronger than grazer limitation across lakes, which was more consistent with the food-web versus food-chain model. Changes in algal composition were also broadly consistent with predictions of the food-web model in that vulnerable, superior nutrient competitors dominated in low productivity lakes and more grazer-resistant species were observed in high productivity lakes. In general, these results point to the importance of examining limiting factors across systems and the consideration of key species’ traits when predicting and interpreting patterns. 相似文献
10.
The up-regulation of secondary metabolic pathways following herbivore attack and the subsequent reduction in herbivore performance have been identified in numerous woody plant species. Eucalypts constitutively express many secondary metabolites in the leaves, including terpenes and formylated phloroglucinol compounds (FPCs). We used clonal ramets from six clones of Eucalyptus grandis and two clones of E. grandis x camaldulensis to determine if methyl jasmonate (MeJA) treatment could induce changes in the foliar concentrations of either of these groups of compounds. We also used bioassays to determine if any changes in the performance of larvae of Paropsis atomaria, a chrysomelid leaf beetle, could be detected in treated ramets versus the untreated controls, thus indicating whether MeJA induced the up-regulation of defences other than terpenes or FPCs. We found no significant effects of MeJA treatment on either the foliar concentrations of terpenes and FPCs or on herbivore performance. We did, however, detect dramatic differences in larval performance between Eucalyptus clones, thereby demonstrating large variations in the levels of constitutive defence. Larval feeding on clones resistant to P. atomaria resulted in high first instar mortality and disruption of normal gregarious feeding behaviour in surviving larvae. Histological examination of larvae feeding on a resistant clone revealed damage to the midgut consistent with the action of a toxin. These findings concur with mounting evidence that most evergreen perennial plants lack foliar-induced defences and suggest that constitutively expressed secondary metabolites other than those commonly examined in studies of interactions between insect herbivores and Eucalyptus may be important in plant defence. 相似文献
11.
Plant species produce litter of varying quality and differ in the quality and quantity of compounds they release from live
roots, which both can induce different decomposer growth in the soil. To test whether differences in decomposer growth can
forecast the amount of N species acquire from plant litter, as suggested by theory, we grew individuals of three grassland
plants—Holcus lanatus, Plantago lanceolata and Lotus corniculatus—in soils into which 15N-labelled litter of either Holcus, Plantago or Lotus was added. We measured the effects of live roots and litter of each species on soil microbes and their protozoan and nematode
feeders, and to link decomposer growth and plant nutrient uptake, we measured the amount of N taken up by plants from the
added litter. We hypothesised that those species that induce the highest growth of microbes, and especially that of microbial
feeders, will also take up the highest amount of N from the litter. We found, however, that although numbers of bacterial-feeding
Protozoa and nematodes were on average lower after addition of Holcus than Plantago or Lotus litter, N uptake was higher from Holcus litter. Further, although the effects on Protozoa and bacterial- and fungal-feeding nematodes did not differ between the
live plants, litter-N uptake differed, with Holcus being the most efficient compared to Plantago and Lotus. Hence, although microbes and their feeders unquestionably control N mineralization in the soil, and their growth differs
among plant species, these differences cannot predict differences in litter-N uptake among plant species. A likely reason
is that for nutrient uptake, other species-specific plant traits, such as litter chemistry, root proliferation ability and
competitiveness for soil N, override in significance the species-specific ability of plants to induce decomposer growth. 相似文献
12.
Correlation between plant size and reproductive output may be modified by herbivory in accordance with host plant density
and the presence of nonhost plants. To elucidate the effects of nonhost plant density and host plant density on the intensity
of herbivory and reproductive output of the host plant in relation to plant size under natural conditions, we investigated
the abundance of three lepidopteran insects, Plutella maculipennis, Anthocharis scolymus, and Pieris rapae the intensity of herbivory, and fruit set of their host plant, Turritis glabra (Cruciferae). To elucidate the effects of nonhost and host plant density, we selected four categories of plots under natural
conditions: low density of nonhost and high density of host plants; low density of both nonhost and host plants; high density
of both nonhost and host plants; and high density of nonhost and low density of host plants. The plant size indicated by stem
diameter was a good predictor of the abundance of all herbivorous species. The effects of density of nonhost and host plants
on the abundance of insects varied among species and stages of insects. As the abundance of insects affected the intensity
of herbivory, herbivory was more apparent on larger host plants in plots with low density of both nonhost and host plants.
Consequently, the correlation between plant size and the number of fruits disappeared in low plots with density of both nonhost
and host plants. In this T. glabra– herbivorous insect system, the density of nonhost plants and host plants plays an important role in modifying the relationship
between plants and herbivores under natural conditions.
Received: July 19, 1999 / Accepted: June 15, 2000 相似文献
13.
We conducted a 20-week manipulative field experiment on shallow forereefs of the Florida Keys to assess the separate and interactive
effects of herbivory and nutrient enrichment on the development of macroalgal communities and the fitness of the corals Porites porites and Siderastrea siderea. Excluding large herbivorous fishes produced macrophyte blooms both with and without nutrient enrichment. In contrast, there
were no direct effects of nutrient enrichment. There were, however, small, but significant, interactive effects of herbivory
and enrichment on macroalgal cover. Following nutrient enrichment, total macroalgae and the common seaweeds Dictyota spp. were suppressed in the presence, but not in the absence, of large herbivorous fishes—suggesting that fishes were selectively
feeding on nutrient-enriched macrophytes. Access by large herbivores prevented algal overgrowth of corals, but these large
fishes also directly grazed both corals. Excluding fishes did not alter survivorship of either coral species, but did decrease
parrotfish grazing scars on both corals and increased the net growth of P. porites. Nutrient additions had no direct effects on the survivorship of corals, but there was a trend (P = 0.097) for nutrients to stimulate the growth of P. porites. The preponderance of experiments available to date indicates that loss of key herbivores is a major factor driving macroalgal
blooms on coral reefs; anthropogenic nutrient pollution generally plays a more minor role. 相似文献
14.
Peter S. Petraitis 《Oecologia》1990,83(3):405-413
Summary The predatory gastropod Nucella lapillus, commonly preys upon the mussel, Mytilus edulis, and is thought to control the distribution and abundance of mussels on the rocky shores of New England, USA. In this study, done in Maine, USA, not only the presence of Nucella lapillus but also the roughness of the experimental surface and the presence of the herbivorous gastropod, Littorina littorea, were manipulated. Four types of surfaces were used as recruitment substrata for mussels: smooth bare granite, aggregations of the barnacle, Semibalanus balanoides, fiberglass resin castings of smooth bare granite and resin castings of aggregations of S. balanoides. To ensure that caged N. lapillus were not starving, barnacles were provided as alternative prey. Experiments showed no detectable effect of N. lapillus on the recruitment of M. edulis. Mussel recruitment was enhanced by surface rugosity and depressed by the activities of L. littorea. Analysis of covariance, using the number of algal species as the covariate, suggested that L. littorea reduced the number of newlyrecruited mussels by removing algae that provided recruitment sites, but no manipulations were done to test this conjecture. It is likely that previous reports of N. lapillus controlling mussel abundance are attributable to N. lapillus preying upon barnacles, which increase surface rugosity and enhance mussel recruitment. Review of literature on feeding preferences of N. lapillus supports this view. When handling times and prey availability are taken into account, Nucella shows a clear preference for barnacles over mussels. 相似文献
15.
Gregory M. Crutsinger Melissa N. Habenicht Aimée T. Classen Jennifer A. Schweitzer Nathan J. Sanders 《Plant and Soil》2008,303(1-2):95-103
Plant–insect interactions can alter ecosystem processes, especially if the insects modify plant architecture, quality, or
the quantity of leaf litter inputs. In this study, we investigated the interactions between the rosette gall midge Rhopalomyia solidaginis and tall goldenrod, Solidago altissima, to quantify the degree to which the midge alters plant architecture and how the galls affect rates of litter decomposition
and nutrient release in an old-field ecosystem. R. solidaginis commonly leads to the formation of a distinct apical rosette gall on S. altissima and approximately 15% of the ramets in a S. altissima patch were galled (range: 3–34%). Aboveground biomass of galled ramets was 60% higher and the leaf area density was four
times greater on galled leaf tissue relative to the portions of the plant that were not affected by the gall. Overall decomposition
rate constants did not differ between galled and ungalled leaf litter. However, leaf-litter mass loss was lower in galled
litter relative to ungalled litter, which was likely driven by modest differences in initial litter chemistry; this effect
diminished after 12 weeks of decomposition in the field. The proportion of N remaining was always higher in galled litter
than in ungalled litter at each collection date indicating differential release of nitrogen in galled leaf litter. Several
studies have shown that plant–insect interactions on woody species can alter ecosystem processes by affecting the quality
or quantity of litter inputs. Our results illustrate how plant–insect interactions in an herbaceous species can affect ecosystem
processes by altering the quality and quantity of litter inputs. Given that S. altissima dominates fields and that R. solidaginis galls are highly abundant throughout eastern North America, these interactions are likely to be important for both the structure
and function of old-field ecosystems. 相似文献
16.
The landscape (matrix) surrounding habitat fragments critically affects the biodiversity of those fragments due to biotic
interchange and physical effects. However, to date, there have been only a limited number of studies on plant–animal interactions
in fragmented landscapes, particularly on how tree seedling herbivory is affected by fragmentation. We have examined this
question in a fog-dependent mosaic of rainforest fragments located on coastal mountaintops of semiarid Chile (30°S), where
the effects of the surrounding semiarid matrix and forest patch size (0.1–22 ha) on tree seedling survival were simultaneously
addressed. The rainforest is strongly dominated by the endemic evergreen tree species Aextoxicon punctatum (Olivillo, approx. 80% of basal area). To assess the magnitudes and causes of Olivillo seedling mortality, we set up a field
experiment where 512 tree seedlings of known age were transplanted into four forest fragments of different sizes in four 1.5 × 3-m
plots per patch; one-half of each plot was fenced off with chicken wire to exclude small mammals. The plots were monitored
for 22 months. Overall, 50% of the plants died during the experiment. The exclusion of small mammals from the plots increased
seedling survival by 25%, with the effect being greater in smaller patches where matrix-dwelling herbivores are more abundant.
This experiment highlights the important role of the surrounding matrix in affecting the persistence of trees in forest fragments.
Because herbivores from the matrix cause greater tree seedling mortality in small patches, their effects must be taken into
account in forest conservation–restoration plans. 相似文献
17.
Herbivory can induce changes in plant traits that may involve both tolerance mechanisms that compensate for biomass loss and
resistance traits that reduce herbivore preference. Seagrasses are marine vascular plants that possess many attributes that
may favour tolerance and compensatory growth, and they are also defended with mechanisms of resistance such as toughness and
secondary metabolites. We quantified phenotypic changes induced by herbivore damage on the temperate seagrass Posidonia oceanica in order to identify specific compensatory and resistance mechanisms in this plant, and to assess any potential trade-offs
between these two strategies of defence. We simulated three natural levels of fish herbivory by repeatedly clipping seagrass
leaves during the summer period of maximum herbivory. Compensatory responses were determined by measuring shoot-specific growth,
photosynthetic rate, and the concentration of nitrogen and carbon resources in leaves and rhizomes. Induced resistance was
determined by measuring the concentration of phenolic secondary metabolites and by assessing the long-term effects of continued
clipping on herbivore feeding preferences using bioassays. Plants showed a significant ability to compensate for low and moderate
losses of leaf biomass by increasing aboveground growth of damaged shoots, but this was not supported by an increase in photosynthetic
capacity. Low levels of herbivory induced compensatory growth without any measurable effects on stored resources. In contrast,
nitrogen reserves in the rhizomes played a crucial role in the plant’s ability to compensate and survive herbivore damage
under moderate and high levels of herbivory, respectively. We found no evidence of inducibility of long-term resistance traits
in response to herbivory. The concentration of phenolics decreased with increasing compensatory growth despite all treatments
having similar carbon leaf content, suggesting reallocation of these compounds towards primary functions such as cell-wall
construction. 相似文献
18.
We examined whether heavy browsing by sika deer, Cervus nippon Temminck, changed morphological characteristics of a Japanese nettle, Urtica thunbergiana Sieb. et Zucc., in Nara Park, where a large population of sika deer has been maintained for more than 1,200 years. Wild nettles
of Nara Park exhibited smaller leaf area, 11–223 times more stinging hairs per leaf, and 58–630-times higher stinging hair
densities than those of other areas where there was no evidence of sika deer browsing. There were no significant differences
in stinging hair length between the areas. Nettles from Nara Park that were cultivated from seeds in a greenhouse retained
a larger number and higher density of stinging hairs. In the field, nettles of Nara Park were less frequently browsed by sika
deer and showed higher survivorship than nettles that were transplanted from an unbrowsed area into Nara Park. These results
indicate that: (1) the U. thunbergiana population of Nara Park has an extremely high stinging hair density compared with those of unbrowsed areas; (2) this characteristic
has a genetic basis, and (3) stinging hairs serve as a defensive structure against sika deer, contributing to an increase
in survivorship. Thus, we conclude that a U. thunbergiana population in Nara Park, with extremely high stinging hair densities, has evolved through natural selection due to heavy
browsing by sika deer. 相似文献
19.
Brage Bremset Hansen Snorre Henriksen Ronny Aanes Bernt-Erik Sæther 《Polar Biology》2007,30(5):549-558
A central challenge in ecology is to predict long-term consequences of high herbivore densities on their resources. Here we
describe vegetation changes during 26 years following the reintroduction of a wild Svalbard reindeer (Rangifer tarandus platyrhynchus) population that was not subject to predation. The population irrupted, crashed and subsequently fluctuated around lower
densities throughout the study period. The irruption generated strong trophic top-down effects on the vegetation including
a decline in the cover of mosses, vascular plants and lichens. Previously dominant fruticose lichens, which are preferred
forage during winter, were almost depleted and showed no response to the relief in grazing pressure. This in turn indirectly
affected rates of recovery in other plant groups subsequent to the crash. Mosses recovered completely and even exceeded pre-reindeer
levels 6 years after the population peak. Recovery of vascular plants was more delayed and only partial due to a long-term
suppression of common species that are important as reindeer forage. Thus, a suppression of major forage species and a sustained
reduction in herbivore densities suggest that overgrazing occurred during the population irruption, possibly inducing a long-term
decline in reindeer carrying capacity K. This supports the “exploitation ecosystem hypothesis” predicting top-down control of vegetation by herbivores when predators
are absent. 相似文献
20.
Disturbances such as fire, grazing, and soil mixing by animals interact to shape vegetation in grassland ecosystems. Animal-generated disturbances are unique in that they arise from a suite of behaviors that are themselves subject to modification by external factors. The manner in which co-occurring animal taxa interact to alter vegetation is a function of their respective behaviors, which shape the characteristics (e.g., the magnitude or extent) of their disturbances. To determine whether prairie dogs (Cynomys ludovicianus) and harvester ants (Pogonomyrmex occidentalis) interactively alter vegetation structure and heterogeneity on the Colorado shortgrass steppe, we characterized the size, dispersion, and vegetation of prairie dog burrow mounds and ant nests (located on and off prairie dog colonies) and vegetation growing beyond mound and nest perimeters. Ants located on prairie dog colonies engineered significantly larger nests and disturbed nearly twice as much total soil area as their off-colony counterparts. Ant nests were overdispersed both on and off prairie dog colonies, while prairie dog mounds were randomly dispersed. Where harvester ants and prairie dogs co-occur, the overdispersed pattern of on-colony ant nests is in effect "overlaid" onto the random pattern of prairie dog mounds, resulting in a unique, aggregated pattern of soil disturbance. Ant nests on prairie dog colonies had significantly less vegetation and lower plant species diversity than did prairie dog mounds, while off-colony nests were similar to mounds. These results suggest that ant nests are more highly disturbed when located on prairie dog colonies. Beyond nests proper, ants did not appear to alter vegetation in a manner distinct from prairie dogs. As such, the interactive effects of prairie dogs and ants on vegetation arise mainly from the disturbance characteristics of mounds and nests proper. 相似文献